Depression is now the leading cause of disability and poor health worldwide, the World Health Organization (WHO) said in a statement Friday. By their estimates, more than 300 million people live with the condition—an 18 percent increase since 2005. But nearly half of these people don't get the treatment they need. "These new figures are a wake-up call for all countries to rethink their approaches to mental health and to treat it with the urgency it deserves," Margaret Chan, WHO director-general, said in the statement.

The WHO also pointed out links between depression and other conditions—like substance use disorders, diabetes, and heart disease. (People with depression are more likely to have these conditions, but people with these conditions are also more likely to have depression— it doesn’t mean that one causes the other.) Depression is also associated with suicide, which kills an estimated 800,000 people each year, according to WHO research.

The WHO has released these figures in the lead-up to World Health Day on April 7. This theme of this year's campaign is "Depression: Let's Talk," which highlights the need to combat the stigma associated with mental health conditions. "For someone living with depression, talking to a person they trust is often the first step towards treatment and recovery," Shekhar Saxena, M.D., director of the WHO Department of Mental Health and Substance Abuse, said in the statement.

Depression is a mental health condition that involves persistent feelings of sadness, anxiety, or emptiness over a 2-week period. Symptoms of depression include loss of interest in daily activities, fatigue, restlessness, difficulty sleeping, or appetite and weight changes.